Apparatus for controlling the operation of gas-filled modulator tubes



June 7, 1960 .1. J. GUARRERA 2,940,049

APPARATUS FOR coNTRoLLTNG THE; OPERATION oT GAS-FILLED MoDuLAToR TUBES Filed May 23, 1955 Tirzi.

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Pu; se' 0 O @iA/Quran 2 4,0) d @4,2 /z 719665@ J r giri/PA 70E INNEN TOR A ORNEYS Patent -f John J. Guarrera, Northridge, Calif., assignor to Reeves Instrument Corporation, New York, N Y., a corporation of New York Filed May 23, 1955, Ser. No. 510,246

S Claims. (Cl. 328-210) This invention relates to thyratron control systems and more specifically to an improved method and apparatus for controlling the operation of thyratrons in order to attain precision operation of one or more tubes and insure stability of operation throughout the life of the tube.

Gas-filled grid-controlled thyratron rectiers which are also referred to as soft tube modulators usually employ a heated cathode, a plate and a control grid as in the case of ordinary vacuum tubes. This tube diers, however, from the conventional vacuum tube in that the current lowing between the heated cathode and the plate jumps, for all practical purposes, from a zero value to a very high value with the application of a predetermined voltage on the grid of the tube. This action is brought about as a result of ionization of the gas within the tube carried by the application of a potential to the control grid. In the case of present thyratrons such as the 4G35, the firing pulse must be applied to the grid for durations of three to ten micro-seconds depending on the characteristics of the individual tube. Thus, in the case of one tube this grid or firing pulse must be applied for a duration of three micro-seconds before the plate current within the tube will rise to its maximum value. In another tube, the required tiring pulse may be of the order of ten micro-seconds. This variation has not only limited the use of soft tube modulators in high-troquency circuits, but in applications requiring the synchronized ring of a plurality of tubes it was diihcult, if not impossible, to re them simultaneously or in other synchronized orders. In addition to the variation -in this long time delay, grid-controlled gas tubes are found to have a rather rapid variation superimposed on the normal anode delay time discussed above so that a tube will not tire in precisely the same way each time a pulse is applied. This variation may be referred to as the pulse-to-pulse jitter time and of course seriously complicates synchronous and parallel operation of tubes.

One object of the invention is to overcome the problems encountered in the operation of thyratrons, and effect precision ring so that the ring of a given tube can be precisely determined and in addition a substantially uniform anode delay time can be secured for all tubes of a given type notwithstanding the inherent pulseto-pulse jitter variations. Another object of the invention is an improved circuit for operating grid-controlled gas thyratrons that will effect in addition to precision control of the tubes very much faster and more uniform operation.

The above and other objects of the invention will become more apparent from the following description and accompanying drawing forming part of this application.

In the drawing:

Fig. 1 is a block diagram illustrating a circuit in -accordance with the invention; and

'ice

Fig. 2 illustrates the application of the circuit of Fig. 1 to the control of two or more tubes.

Broadly, this invention concerns an improved circuit and system for firing thyratrons to shorten the anode delay or tiring time and to attain precision `operation of circuits to be controlled thereby. In the drawing, a thyratron or soft tube modulator is denoted'generally by the numeral 10 and includes a cathode 12, a plate I 14, a grid 16 and a filament 18. The iilament is normally heated by a suitable source of power connected to the terminals 20 and 22. Firing pulses for tiring the tube may be generated by any suitable electronic equipment and is diagrammatically illustrated herein by the rectangle 24 which is connected by the leads 26 and 28 to the grid 16' and ground,.respectively. For convenience the cathode 12 is also shown as connected to ground by means of the lead 30. The load, or that equipment, which is to be operated by the thyratron is denoted broadly by the rect-angle 32 which is connected yby leads 34 and 36 to the plate 14 and ground, respectively.

As is well known, the -ring of a gas-controlled tube takes the form of a chain reaction which occurs after thepotential applied to the grid has reached a value where plate current will begin to ow. At this point ionization begins to take place and it is normally completed in the order of three to ten micro-seconds. It has been vfound that this ionization or anode delay time can be materially reduced by arranging the pulse generator 24 to produce two successive pulses having predetermined characteristics for this purpose. The initial pulse applied to the grid 16 should preferably be of a Value that does not permit the tube 10 to tire and is termed apre-trigger pulse. This pulse functions to condition the tube for a second pulse that may follow the application of the rst pulse by one or more microseconds. The second or tiring pulse is preferably quite narrow and having a very fast rise time and an amplitude of the order of that required to re the particular tube. With this system the firing of the thyratron is virtually coincident with the application of the second or firing pulse so that extremely high degrees in accuracy can be attained in controlling the precise timev of tiring of the tube.

This procedure is particularly useful in connection with the tiring of two or more thyratrons simultaneously, in whichmcase a circuit broadly illustrated in Fig. 2 may vbe employed. In this embodiment of the'invention the thyratrons are denoted by the numerals 10 and 10. Corresponding elements in each gure are denoted by like numerals with the numerals in Fig. 2 being primed. The pulse generator 24 in this form of the invention is connected to the grids 16 and 16 through se ries resistors 38 and 38 and is arranged to generate the rst or pre-trigger pulse which conditions the thyratrons prior to the application of the trigger pulse. The trigger generator 40, which may be formed as part of the generator 24', applies the trigger pulse individually to the grids 1-6ar1d 16' through resistors 42 and 42 to ef-v fect substantially instantaneous tiring of both tubes.- While the precise circuits of the pulse `generators 24,`

24' and 40 are not shown, procedures for developing these pulses are so well known in the art that it was felt that their illustration and description would result in unnecessary complication of the application and therefore have been omitted.

The loads 32 and 32 which are controlled by the, thyratrons have merely been shown diagrammatically.

equipment employing the Vconventional 1magnetron Vc )slil-g pedanceof ythe thyratrons. trons, it is'desirable 'to use pulse Y lator or the rectification of alternating current-topm- `vide controlled D.C. potentials and the like.

Here again, the utilization of thyratrons forthese purposes isz-so 'well-knovvniniheartthatit is felt vthat Yanyfurther showing would only serve to Vcomplicate rather than clarify theinventio'n` Y Y A Tire method of "electingprecision' firing of thyratrons 'as described Eabove reduces thev pulse-to-ptilse jitter lto a negligiblevalueand while insuring uniformity choperation lof Vtubes-land therefore facilitating the replacement thereof without'dis'turbingthe operation oftheapparatus does not function 5to materially shorten the anode delay Aa cathode, a control electrode, and an anode, means coupling the cathodes of said tubes to a common terminal, means including a load coupled` between said common terminal andthe anodes of said tubes, a rst pulse generator having a pair of output terminals, one of said terminals being lcoupled toV said common terminal, rst resistor means 'coupled between vthe'other"terminal of said first pulse generator and the"control electrode of said first thyravtron, second resistor means coupled 'betweenthe 'other terminal of said irst pulse generator and v the control Velectrode'of said second thyratron, .a second pulselgenerator having a pair of output terminals, one

time `aspreviously discussed. Shortening of this delay timefmay be accomplished, however, by theutilizationof anfimproved. forcetring procedurerwherein the pulse gen- Y eratoriof Fig-f1 lisarran'g'ed to provide aV pulse 'of Y extremely large magnitude-and* of such .a .naturej that ittwill:forcelionizationJ to 'take A.place within lanY extremely shortatimef-In ithe fcase of-'the 4G35 thyratron, it 'has been found ithatb'yV arranging the pulse .generator'24 fto produce-a grid pulse of the order of 1,000 yto. 2,000 volts fora-.duration of '.05 .to .15 microfsecond duration that theanodedelay timeo'f .thethyratron can be'reduced tothe order of .05 micro-second'as compared with the'nor# maldelay time -ofpthree to Vten micro-seconds. The Aappiieationzofzthes'e Vhigh voltagesvto thegrid of the thyraltren has 'not been found to Vadversely affect `tlubedn anyway, but on the other hand hasactually resulted in attaining substantially uniform operation 'of the tube throughout its'entire life. /Moreoven the pulse-topulse jitterV variation -which ,heretofore constituted a serious Yproblem in the utilization of tubes ofrtlu'sV character is also` reduced to ja Ynegligible value not measurable .by

rmetho'ds heretofore used for this purpose. Actu'altestsYY Y have indicatednhat with the forcedrring procedure asY describedabove, variationsbetween dierent tubes have been lessrthan .0l Vmicro-second, whereas, under normal conditions itlis exceedingly diicult even with careful` tube selection methods to maintain these variations within Z'Sfmicro-second. i Y Y inY 'order zto .obtain the greatest precision i inthe tiring offthev thyratrons, the internal impedance of the pulse generators 24 Yand 4ii'in Figs. l and 2, respectively, should be relatively'lbw'as compared witlithe grid circuitim- With conventional thyragenerators havinginterf nai impedans of so'nhmsor less.

Y, It `has been Yfound that when a pulsegenerator" having anjim'pedance or" 50 ohms'is operated into the grid circuitVr 'o'f Va 'thyratron."having ari-impedance in eXcess vorf- 5'0O-ohms"the vpulsefwill have Vva tendency to rise to almost doubleY its jnominalY output. This will produce 'a' somewhatiasterriseon'the leading edge "of thepulse pulse-topulse jitter.

Where aprejtrigger pulse' is Vapplied 'das' iii1`Fig.V 2, it VisVY desirable that the :internal impedance of the'V Vpre-trigger p' pulsef'surce befairl'y high,jsay, on fthe order of 110.00V ohmsorfmore. Howes/er, the impedance of the trigger pulse source should below and preferablyY on the order ofY 50 ohms-for conventional thyratrons.V Y Y Y :Whilew two-differentrsystems have been described 'for attaining'the objects of this invention, they both function to'increase therate of ionization -o/the gas within the tube in such a manne-r that the time of Afiring can be precisely controlled without adversely aiecting the tube. `lY/Ioreover, AVext-r'en'tely'highV `tube stability is obtained Vthroughoutitsnormal life.

Y While-only-certainembodiments of thisinvention have n been Yillustrated and described, itis apparent that modi-Y 'iicationaV A:alterations'fandl'changes may lbe made without departing @fronti the true -scope'fand :spirit thereof.

what :claimed is;

andthusfpwu alshert anode delay` time and eliminate' Y of said terminals being coupled to Vsaid common terminal, third resistor means coupled between the other terminal of said second pulse generator and Y,the control electrode of said r-st thyratron, and fourth'resistor means coupled t betwcenthe other terminal of said second pulse Vgenerator and Vthe control electrode lof said second'thyratron, said VVfirst and second pulse V`generators producing coincident gas-filled tubes each having at least an anode,'a cathode,

and a control electrode, comprising in combination, load circuit means coupled to the anodes of said plurality of gas-filled tubes, a rst pulse generating means coupled between each of. the control electrodes of saidtubes and the'cathodes of said tubes, said first 'pulse generating means producing rst recurrent positive pre-ionization pulses having a magnitude insuilcient to cause any of said tubes to tire, andsecond Ypulse generating'means coupled between each of the control electrodes Vof said tubes and the cathodes of said tubes, said secondApulse generating' means producing second recurrent positive trigger pulses havingl a magnitude larger'thanthemagnituderof said first recurrent pulsesV for simultaneously tiring said `plurality ofV .gas-.filled tubes, said second recurrent trigger pulses,occurringjimmediately following the application of said rst recurrent Apre-ionization pulses to the` control electrodes 'of saidtubes; .i

' `5.. .I`he system as dened by claim '.4 whereinthe duration .of said rst recurrent pre-ionization pulses produced byaid .Yiirst pulseV generating means is longer than the Y vduration of said secondrecurrenttrigger pulses produced byfsaidfsecond pulse igeneratingrmeans. Y

` 6.Y A systent for simultaneously ringauplurality of gas-'lled tubes 'each having at least an anode, Vacatltode,

and YVa'control Velectrode comprising'in combination, first means coupled'to the control electrodes of said plurality of gaslledtubes for supplying rstprecurrentipositive pre-ionization pulses theretovhaving a magnitude insuficient'to cause any of said tubes to conduct, and second means coupled to the controlelectrodes ofsaid' pluralityV ofgasllled vtubes for .supplying second recurrent posi- Y tive triggerpulses thereto, said-second'recurrenttrigger pulses having avduration less than the duration ofY said rstfaecurrent pulses and occurring immediately `:following .said first recurrent pulses. Y Y

7. AA system forsimultaneously .firing a v plurality of gas-filled tubes each'having an input circuit and au output circuit comprising in combination, rst means coupled to the input Vcircuits of said". plurality 'of gas-lilledrtubes Vfor supplying pirrst recurrent pre-ioniiation pulses thereto Y having a magnitude insuiient to cause any ofsaidltl'lbresv Y to conduct, and second means coupled-tothe input Leircuitsi'of -saidpluralityfof gas-lled Vtubes fonsupplyingV second recurrent triggerVv pulses lthereto,=said Ysecond Y'reof-the pulses from 

